Effect of Fluid Flow on Removal of Dissolution Products from Small Cavities

The effect of fluid flow on transport of reaction products from dissolving cavities was investigated theoretically in order to establish regions of parameter space where the solution within the cavity may be above, or below, the saturation concentration. Situations where such phenomena are important include etching of masked devices and pitting corrosion. Steady laminar convective transport was analyzed in smooth-walled two-dimensional cavities (trenches) of several shapes. The fluid flow patterns within the cavities were obtained in the Stokes flow region. The convective diffusion problem was solved for values of the Peclet number between 1 and 500. Two types of boundary conditions were investigated: (i) uniform dissolution of the cavity surface, and (ii) uniform concentration along the cavity surface. Numerical calculations were carried out with a commercial, general-purpose finite element code. It was found that for Pe ≤ 1, the entire cavity volume had a concentration in excess of 90% of the saturation value while for Pe ≥ 100, the electrolyte within the cavity was substantially free of dissolution products.